The present invention relates to a flat package for a semiconductor IC (Integrated Circuit) and, more particularly, to a quad flat package having leads extending out in four directions.
A flat package for a semiconductor IC is disclosed in, for example, "LSI Handbook" compiled by the Institute of Electronic and Communication Engineers of Japan and published by Ohm Sha, 1984, pp. 414-415. This document shows, particularly in FIG. 3.62, a typical surface mounting package having leads extending out from all the four sides thereof. This type of package is generally referred to as a quad flat package (QFP). A flat package has been developed to implement the miniaturization and advanced functions of various kinds of electronic apparatuses, and is extensively used today. A QFP in particular facilitates impedance matching because it has a substantially square contour, i.e., all the wirings in the package have substantially the same length. For this reason, QFPs are extensively applied to, for example, logical circuits needing high-speed performance. Preferably, therefore, a semiconductor chip mounted on the package should be shielded in order to be immune to external electromagnetic fields and to radiate no needless electromagnetic waves to the outside, i.e., to enhance the electromagnetic wave interference (EMI) characteristic. However, it is impossible to meet the users' different needs relating to the shield connection with a single standard type of ICs without limiting the number of valid leads.